# Implement derivative transfer function (numerator greater order than denominator) in Simulink

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Mike Buba on 14 May 2020
Commented: Gautam on 17 May 2020
How to implement derivative transfer function (numerator greater order than denominator) in Simulink?
Briefly, I am developing a three-phase inverter control in dq frame and have load current for the inverter model. The same current is a feedforward signal for the control. To compensate for disturbance (as per theory), the compensator transfer function should be inverse of the closed-loop controller and plant:
This is a second-order transfer function. Inverse has higher-order numerator than denominator. How to implement this in Simulink. Block Transfer Fcn has condition 'The order of the denominator must be greater than or equal to the order of the numerator'.
My model is in a continuous environment.
Can I implement a derivative-based transfer function (numerator greater order than denominator) in discrete?
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Gautam on 17 May 2020
Yes, however you have to do a little manipulation of the trasfer function before implementing. Discretise the transfer function(use c2d in MATLAB to get discrete transfer function, take care of the sample time for discretizing so that the discrete system response is similar to the continuous system OR you can try pen&paper and derive analytically), convert it to a difference equation(pen and paper-> basically find the discrete time domain equation) and implement the difference equation in Simulink.

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